Hopefully I can add a little here and maybe save you a headache or two.. IMO, 6.5" of lift for your planned wheeling isn't really needed for numerous reasons. Since you mentioned the budget, I've learned the higher you want to go - the higher the budget goes.
The taller the leaf springs, the harsher they tend to ride. It will push the OEM steering design and driveline angles to the max.
I've owned XJ's for twenty years and had many different suspension configurations. I've been at 5.5" running 35" tires for 10 years now, and this rig has walked right up Sledgehammer in JV without an ounce of problems - but honestly, an XJ with 4-4.5" and 33's can do some amazing things, including your planned weekend wheeling and save your budget, remain very comfortable and reliable on the street too.
Maybe ditch the RC coils for something slightly taller or add a small spacer if you like their performance. I'd ditch the add a leaf and block. Generally they ride poorly and the blocks promote axle wrap, which will fatigue the OEM springs even faster. A full replacement pack is a better idea. As I mentioned about budget - Deaver Spring or National Spring make some of the best, are not cheap, but you get what you pay for. I'm still running the same Nationals 10 years later.
Sorry to ramble, hope some of this is useful to you...